Any saw you buy now, you should go for the professional series. Yes it will cost much more but you will have a saw for life and one that does what you want. Dolmar is the biggest bang for the buck. One of the most versatile all around saws that will drive up to a 20" bar is a used Husky 257 or 357XP. New, the 357 cost over $600. Pro model Stihls will be up there as well. Last place I'd buy a chainsaw from is a box store. There is more to a saw than
hp however. One of the largest factors is the piston weight and makes a difference in the inertial forces of the chain saw and its ability to cut when pressure is applied. It also has much to do with the speed of the saw. Lighter piston saws such as the older Husky 262 revved up very fast but you have to be diligent with its saw chain sharpening and use a little lighter touch. Cuts like a banshee however when run correctly. If I had to have one saw ( I have 8) it would be a 257 or 357 with both a 16" and 20" bar.
Model numbers of saws do not always relate to more power but may be more in line with where they sell the saw for instance a pro 357 Husky is more powerful than the box store 455